media: ddbridge: improve error handling logic on fe attach failures

This change makes sure that demod frontends are always detached whenever
a tuner frontend attach failed. Achieve this by moving the detach-on-
failure logic at the end of dvb_input_attach(), and adding a goto to this
block on every tuner attach failure case, so if an error occurs, there are
no stray attached frontends left. As a side effect, this removes some
duplicated code.

Signed-off-by: Daniel Scheller <d.scheller@gmx.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>